Human prostatic acid phosphatase (ACPP) has been used as a tumor diagnostic marker and was shown to possess tyrosine phosphatase (PTPase) activity. In order to study the protein structure-function relationship of the enzyme and the mechanisms of its androgen regulation, we have undertaken protein sequencing, cDNA cloning, characterizing genomic organization, and expression of the ACCP gene in neoplastic and benign tissues. The ACPP gene has been mapped by fluorescence in situ hybridization to chromosome 3q21-23 and its protein-encoding sequence is interrupted by nine introns. The expression using northern blot analysis of ACPP gene, as well as prostate specific antigen, glyceraldehyde-3- phosphate dehydrogenase and lactate dehydrogenase-A(muscle) genes, was elevated significantly in prostatic carcinoma when compared with the expressions of these genes in benign prostatic hyperplasia in the same patient.